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An Endopolygalacturonase from Sclerotinia sclerotiorum Induces Calcium-Mediated Signaling and Programmed Cell Death in Soybean Cells

August 2005 , Volume 18 , Number  8
Pages  849 - 855

Anna Zuppini , 1 Lorella Navazio , 1 Luca Sella , 2 Carala Castiglioni , 2 Francesco Favaron , 2 and Paola Mariani 1

1Dipartimento di Biologia, Università di Padova, via U. Bassi 58/B, 35131 Padova, Italy; 2Dipartimento Te. S.A.F., Sez. Patologia Vegetale, Università di Padova, Viale dell'Università 16, 35020 Legnaro, Padova, Italy

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Accepted 5 April 2005.

A basic endopolygalacturonase (PG) isoform, produced early by Sclerotinia sclerotiorum when infecting soybean seedlings, was used to examine the signaling role of the enzyme in aequorin-expressing soybean cells. A cytosolic Ca2+ elevation was induced, with a rapid increase (phase 1) and a very slow decrease (phase 2) of Ca2+ concentration, indicating the involvement of Ca2+ ions in PG signaling. Within 1 h of PG-cell contact a remarkable level of cell death was recorded, significantly higher than the control cell culture turnover. The observed morphological and biochemical changes were indicative of the activation of programmed cell death; in particular, cytochrome c release in the cytoplasm and activation of both caspase 9-like and caspase 3-like proteases were found. When a polygalacturonase-inhibiting protein (PGIP) and the PG were simultaneously applied to cells, both the Ca2+ increase and cell death were annulled. The possible roles of prolonged sustained cytosolic Ca2+ concentrations in inducing cell death and of the PG-PGIP interaction in preventing PG signaling are discussed.

Additional keywords: fungal hydrolytic enzyme .

© 2005 The American Phytopathological Society